1. Field of the Invention
The present invention relates to a magnetic disk device, and more particularly, to a magnetic disk device capable of substantially reducing the deviation of magnetic disks in a radial direction due to a change in ambient temperature, thus preventing the tracks of the magnetic disks from misaligning with the magnetic heads which read the disks.
2. Description of the Related Art
In general, a conventional magnetic disk device has a servo head for positioning magnetic heads, including a data head, relative to respective magnetic disks, and controls such positioning based on servo information read out from the magnetic disks by the servo head. An error in the relative position of the servo head and the data head for reading and writing data to and from a disk is known as an off-track condition, which is the deviation between an expected tracking position and an actual tracking position. Accordingly, the positioning is more accurate when this off-track condition is small.
In the conventional magnetic disk device, undesirable off-track conditions occur due to various factors. In particular, an off-track condition known as a thermal off-track condition is caused by a change in temperature in the magnetic disk device itself, or a change in the ambient temperature. This thermal off-track condition occurs primarily due to differences in the linear expansion coefficient between the constituent elements of the magnetic disk device.
As shown in FIG. 1, the conventional magnetic disk device has a spindle hub 103, fixed to a spindle shaft 105 which is inserted in a base plate 107 and rotatably supported by bearings 106. Magnetic disks 101 and spacer rings 102 are alternately stacked on the spindle hub 103 in an axial direction and fixed directly to an outer peripheral side of the spindle hub 103. Clamp ring 104 secures the magnetic disks 101 and the spacer rings 102 to the spindle hub 103.
In particular, as shown in FIG. 2, in the conventional magnetic disk device, the magnetic disks 101 and spacer rings 102 are alternately stacked and fixed to the spindle hub 103 by the clamp ring 104 while they directly contact the outer periphery of the spindle hub 103. Further, magnetic heads 108, corresponding to the magnetic disks 101, are mounted at one end of the positioner 109 which positions the magnetic heads 108 relative to their respective magnetic disks 101.
In the conventional magnetic disk device, since the magnetic disks 101 and the spacer rings 102 are directly in contact with the outer periphery of the spindle hub 103 when mounted thereto, displacement or deformation of the magnetic disks 101 in a radial direction easily occurs when the shape of the spindle hub 103 changes due to ambient temperature changes or the like.
For example, a conventional magnetic disk device is usually used in a ambient temperature ranging from -40.degree. C. to 60.degree. C. Hence, since the magnetic disks 101, the spacer rings 102 and the spindle hub 103 are in contact with each other and each made of different material, due to the difference in their thermal linear expansion coefficients, when the ambient temperature changes, displacement or deformation of the magnetic disks 101 can occur at the point at which they contact the spindle hub 103 and rings 102. Therefore, the irreversible deviation of the relative position of servo positioning data recorded on the servo information recording surface of the magnetic disks 101 and data recorded on the data recording surface of the magnetic disks 101 by a data head occurs, thus resulting in data read errors when the magnetic heads 108 attempt to read the data on the disks.